The present invention is directed generally to varnishes and, more particularly, to electrically insulating varnishes, methods of making such varnishes and electrical components produced therefrom.
Historically, polyester-based varnishes and epoxy-based varnishes have been the most commonly utilized materials in the area of insulating varnishes for electrical applications. Each of these systems comes to the marketplace with a distinctive set of properties which determines both the advantages and the limitations of the systems.
A myriad of formulations exists for both polyester and epoxy based insulating varnishes. Many formulation modifications to these systems have been successful in slightly improving specific targeted properties. However, none of the commercially available varnishes have been able to satisfy the desire for a "universal varnish", i.e., a varnish having the ideal properties of both epoxy and polyester systems and can be applied by a variety of methods (vacuum pressure impregnation (VPI), dip, trickle, etc.).
Polyester-based electrical varnishes have become very popular and are widely used because of their numerous desirable qualities. The desirable qualities of polyester-based systems include excellent electrical properties, low cost, good thermal endurance ratings, ideal flexibility and moderate bond strengths. However, polyester based varnishes do have weaknesses, which include low chemical and moisture resistance and a tendency toward a low film build.
Epoxy based electrical varnishes complement the desirable qualities of polyester varnishes, especially in the area of high chemical and moisture resistance, impact strength, and high bond strength. The weaknesses associated with epoxy varnishes include higher cost, shorter pot life for some catalyzed systems, lower thermal endurance ratings and less advantageous electrical properties.
In addition to pure polyester and epoxy varnishes, low level modified systems and polymer "blends" have been developed in the prior art with only limited success. Polymer blends usually retain to some extent the disadvantages of the polymer chemistry of the individual systems. Low level modifications generally offer slight improvements in targeted properties.
As a result of the weaknesses of prior art insulating varnishes, electrical components which are coated with the varnishes suffer from the same weaknesses.
In view of these and other shortcomings with prior art varnish compositions and electrical components employing the varnishes, there is a need for varnishes that provide electrical versatility for insulating electrical components.